The invention concerns a heat exchanger system through which a liquid is intended to flow, the heat exchanger system being of the type comprising a heat exchanger with a liquid inlet and a liquid outlet. In operation, this heat exchanger is passed through, on one hand, by fuel coming from the airplane's tank, this fuel passing through said liquid inlet and outlet, and, on the other hand, by the oil from the lubrication circuit of the airplane's integrated drive generator (IDG), this oil passing through other liquid inlets and outlets of the exchanger.
Said fuel having a temperature lower than that of the oil (which heats in contact with the IDG), the heat exchanger makes it possible to cool the oil.
The following is focused, more particularly, on the fuel circuit passing through the exchanger.
The clogging of the exchanger, due to the impurities (also called contaminants) present in the fuel, is a dormant breakdown that can occur at any moment after a certain operating time of the jet engine. Partial clogging of the exchanger would cause head losses that could disrupt the proper operation of the elements of the circuit situated downstream from the exchanger, and total clogging of the exchanger would cut the fuel circuit and therefore cause the jet engine to stop.
Among the different known types of heat exchanger that can be used in a jet engine fuel circuit, we distinguish tube exchangers and plate exchangers.
Tube exchangers have a matrix formed by a network of tubes that separate the two liquids passing through the exchanger. The passage section of the tubes must meet feasibility constraints. In other words, below a minimum inner diameter of the tubes, these tubes are too difficult to manufacture. This minimum inner diameter is often clearly greater than the diameter of the impurities present in the fuel, such that the risk of clogging of this type of exchanger remains low, without, however, being nonexistent. However, in order to increase the thermal performance of a tube exchanger, the tubes generally have pins on their inner surfaces. However, these pins catch the impurities and the impurities caught in the pins move and gradually wear the tube down until it becomes perforated. Such a perforation can have dramatic consequences.
Plate exchangers have the advantage of being able to have liquid passage sections smaller than those of tube exchangers, but the smaller the passage sections, the more the risk of clogging increases. Thus, plate exchangers are used little, if at all, in jet engine fuel circuits today.
Regardless of the type of exchanger used, it is preferable not to have to monitor the clogging of the exchanger. This lack of monitoring requires that one protect against clogging of the exchanger. Thus, the liquid passage sections in the exchanger are provided to be larger than the size of the biggest impurities that may be contained in the liquid. This is why these passage sections are generally significant.